High performance elastic composite materials made from high molecular weight thermoplastic triblock elastomers

ABSTRACT

The present invention comprises a continuous feed spun bonded laminate having improved elastic properties measured at body temperature. The laminate comprises at least one first and second nonelastic layers between which is sandwiched at least one elastic layer, the elastic layer being comprised of a triblock polystyrene-poly(ethylene/propylene)-polystyrene (“SEPS”) copolymer having a number average molecular weight of about 81,000 g/mol. The weight percent of styrene is approximately 18% and the weight percent of ethylene/propylene is approximately 82%. The molecular weight increase in the EP block, while holding the molecular weight of the styrene block constant, increases the entanglement density, polymer chain persistence length and the relaxation time. The resulting laminate load decay rate and load loss measurements over a period of 12 hours at body temperature showed marked improvement over known CFSBL product. The laminate is particularly useful as side panel material in training pants because of the resistance to sagging at body temperature.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of copending provisional patentapplication Ser. No. 60/064,554, filed Oct. 3, 1997, entitled HIGHPERFORMANCE ELASTIC COMPOSITE MATERIALS MADE FROM HIGH MOLECULAR WEIGHTTHERMOPLASTIC TRIBLOCK ELASTOMERS commonly assigned to the assignee ofthe present invention.

FIELD OF THE INVENTION

[0002] The present invention relates to composite elastic materialsproduced from polymers whose number and/or weight average molecularweight is characterized as the entanglement molecular weight, which isalso a function of the microstructure of the polymer in a continuousfilament stretch bonded laminate process. More particularly, the presentinvention relates to a nonwoven laminate of continuous filaments bondedto a meltblown layer, both of these layers being stretched and bondedbetween two layers of spunbonded material, the resulting web beingrelaxed prior to being wound on a takeup roll. The material is useful asside panels in training pants, and other articles where elastic materialcapable of prolonged performance at body temperature.

BACKGROUND

[0003] A key aspect of a disposable garment is fit over time at usetemperature, i.e., the body temperature. Therefore, elastic propertiesare measured at body temperature to simulate the expected end useconditions. Such garments often include portions which are subject torepeated stretch and relaxation stresses over an extended period oftime. Examples include garment materials, pads, wound dressings andwraps, diapers and personal care products where elasticity may bedesired. A particular example is the side panel of training pants andincontinence undergarments. This side panel is typically made of anelastic material, often a composite, which can withstand the repeatedstretch and resulting stress at body temperature.

[0004] At body temperature certain elastic properties of polymers becomeimportant. Two specific elastic properties measured are the rate of loaddecay and the load loss observed over a period of twelve hours at bodytemperature.

[0005] A conventional method of forming such elastic composite materialis one in which nonelastic spunbond facing materials are combined withan elastomer layer, comprised of high performance elastic strands. Thelaminate of the elastic strands is made by; bonding the strand to thefacings using a meltblown polymer containing a tackifier and/or apressure sensitive adhesive. This produces a nonwoven elastic compositewith desirable elongations, along with improved mechanical and bodyconformance properties. This process is sometimes known as a continuousfilament stretch bonded laminate (“CFSBL”) process.

SUMMARY OF THE INVENTION

[0006] The present invention comprises a continuous feed spun bondedlaminate having improved elastic properties measured at bodytemperature. In a preferred embodiment the laminate comprises a layer offilaments formed by a continuous filament process, to which is bonded alayer of meltblown fibers. This composite material is then sandwichedbetween two layers of spunbond fibers after being stretched. Theresulting layers are then passed between a pair of niprolls and theresulting laminate is then relaxed prior to winding on a takeup roll.

[0007] A unique feature of the present invention is the incorporation ofa triblock copolymer as the filament layer. The triblock polymer ispreferably of a triblockpolystyrene-poly(ethylene/propylene)-polystyrene (“SEPS”) copolymer or apolystyrene-poly(ethylene/butylene)-polystyrene (“SEBS”) copolymer, eachhaving a number average molecular weight of about 81,000 g/mol. Theweight percent of styrene is approximately 18% and the weight percent ofethylene/propylene is approximately 82%. Conventional triblock polymeris typically in the 61,000 g/mol range. The molecular weight increase inthe polymer midblock, while holding the molecular weight of the styreneblock constant, increases the entanglement density, polymer chainpersistence length and the relaxation time. The resulting laminate loaddecay rate and load loss measurements over a period of 12 hours at bodytemperature showed marked improvement over known CFSBL product. Thelaminate is particularly useful as side panel material in training pantsbecause of the resistance to sagging at body temperature.

[0008] Other objects, features, and advantages of the present inventionwill become apparent upon reading the following detailed description ofembodiments of the invention, when taken in conjunction with theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention is illustrated in the drawings in which likereference characters designate the same or similar parts throughout theseveral figures of which:

[0010]FIG. 1 is an isometric view of an apparatus for forming acontinuous filament stretch bonded laminate of the present invention.

[0011]FIG. 2 is a table setting forth the process parameters forformation of the Samples used in Example 1.

[0012] FIGS. 3-5 show various process parameters for different materialruns.

[0013]FIG. 6 is a graph of storage modulus plotted against temperatureand the tangent delta.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Definitions

[0015] “Block copolymer” is a polymer in which dissimilar polymersegments are connected by a co-valent bond. Thus AAA . . . BBB . . .gives a diblock copolymer of two dissimilar polymers AAA . . . and BBB .. .

[0016] “Persistence length” shall mean the average chain length at whichthe correlation interaction between two adjacent, generally parallel,polymer chains dies out.

[0017] “Entanglement density” shall mean the number of entanglements ina unit volume of a polymer. Entanglement can result from physicalsegmental entanglement of the polymer molecules, or from polymerssegmental interaction of the polymers by intermolecular force.

[0018] “Relaxation time” shall mean the characteristic time at which 37%of the initial load is lost in a stress-relaxation experiment (asdescribed in further detail hereinbelow).

[0019] “Percent load loss” shall mean the ratio of the differencebetween the initial load and the load at any time divided by the initialload, multiplied by 100.

[0020] “Load response” shall mean the load measured in units of force(grams force pounds) as a function of stretch.

[0021] “Meltblown fibers “shall mean fibers formed by extruding a moltenthermoplastic material through a plurality of fine, usually circular,die capillaries as molten threads or filaments into converging highvelocity gas (e.g., air) streams which attenuate the filaments of moltenthermoplastic material to reduce their diameter, which may be tomicrofiber diameter. Thereafter, the meltblown fibers are carried by thehigh velocity gas stream and are deposited on a collecting surface toform a web of randomly disbursed meltblown fibers. Such a process isdisclosed, for example, in U.S. Pat. No. 3,849,241 to Buntin. Meltblownfibers are microfibers which may be continuous or discontinuous, aregenerally smaller than 10 microns in average diameter, and are generallytacky when deposited onto a collecting surface.

[0022] Detailed Description

[0023] The present invention comprises a continuous feed spun bondedlaminate fabric having improved elastic properties measured at bodytemperature. A novel aspect of the fabric of the present invention isthe incorporation of a high molecular weight triblock copolymer in thecontinuous filament layer. In a preferred embodiment the laminate fabriccomprises a continuous filament layer which is bonded to a meltblownlayer. This intermediate composite is stretched and then laminatedbetween two layers of spunbond material. The spunbond layers can beprovided from supply rolls or formed during the CFSBL process.

[0024] The laminate comprises at least one elastic layer comprised of atriblock polystyrene-poly(ethylene/propylene)-polystyrene (“SEPS”) or atriblock polystyrene-poly(ethylene/butylene)-polystyrene (“SEBS”)copolymer having a number average molecular weight of about 81,000g/mol. A range of molecular weight is usable, depending on what specificpolymer is used. The practical upper limit of the molecular weight,typically expressed as a number average molecular weight is whereviscosity of the polymer prevents extrusion by an appropriate die. Themolecular weight range of the triblock copolymer of the presentinvention can be in the range of about 65,000 to about 100,000 g/mol,more preferably, from about 75,000 to about 90,000 g/mol, and still morepreferably, about 81,000 g/mol. Different polymers produce differentresults, and different uses and projected body temperatures may requiredifferent molecular weights being used. For example, use of the fabricin a training pants for children may be subject to a different bodytemperature than use in winter clothing intended to be underneathseveral layers of clothing without significant air circulation andhigher temperature. Differences in use conditions and repeated stressmay also dictate the type of polymer and molecular weight that producesthe optimal fabric.

[0025] The weight percent of styrene is approximately 18% and the weightpercent of ethylene/propylene is approximately 82%. The molecular weightincrease in the EP midblock, while holding the molecular weight of thestyrene block constant, increases the entanglement density, polymerchain persistence length and the relaxation time. The resulting laminateload decay rate and load loss measurements over a period of 12 hours atbody temperature showed marked improvement over known CFSBL product. Thelaminate is particularly useful as side panel material in training pantsbecause of the resistance to sagging at body temperature.

[0026] The practical upper limit on the molecular weight of the midblockof the triblock polymer is where the viscosity prevents extrusion intofilaments.

[0027] Elastomeric thermoplastic polymers useful in the practice of thisinvention may be those made from block copolymers such as polyurethanes,copolyether esters, polyamide polyether block copolymers, ethylene vinylacetates (EVA), block copolymers having the general formula A-B-A′ or(A-B)_(m), such as, but not limited to,copoly(styrene/ethylene-butylene),polystyrene-poly(ethylene-propylene)-polystyrene,(polystyrene/poly(ethylene-butylene)/polystyrene,poly(styrene/ethylene-butylene/styrene), EPDM rubbers, ethylene-ethylacrylate (EEA), ethylene acrylic acid (EAA), ethylene methyl acrylate(EMA), and the like.

[0028] Useful elastomeric resins include block copolymers having thegeneral formula A-B-A′, where A and A′ are each a thermoplastic polymerendblock which contains a styrenic moiety such as a poly (vinyl arene)and where B is an elastomeric polymer midblock such as a conjugateddiene or a lower alkene polymer. A and A′ can be the same or different.Can also be conjugated dienes as well as the saturated counterpart ofthe conjugated dienes. Block copolymers of the A-B-A′ type can havedifferent or the same thermoplastic block polymers for the A and A′blocks, and the present block copolymers are intended to embrace linear,branched and radial block copolymers. In this regard, the radial blockcopolymers may be designated—(A-B)_(m)—X, wherein X is a polyfunctionalatom or molecule and in which each —(A-B)_(m)—radiates from X in a waythat A is an endblock. In the radial block copolymer, X may be anorganic or inorganic polyfunctional atom or molecule and m is an integerhaving the same value as the functional group originally present in X.It is usually at least 3, and is frequently 4 or 5, but not limitedthereto. Thus, in the present invention, the expression “blockcopolymer,” and particularly “A-B-A′” copolymer, is intended to embraceall block copolymers having such rubbery blocks and thermoplastic blocksas discussed above, which can be extruded (e.g., by meltblowing), andwithout limitation as to the number of blocks. The elastomeric nonwovenweb may be formed from, for example, elastomeric(polystyrene/poly(ethylene-butylene)/polystyrene) block copolymers.Commercial examples of such elastomeric copolymers are, for example,those known as KRATON® materials which are available from Shell ChemicalCompany of Houston, Texas. KRATON® block copolymers are available inseveral different formulations, a number of which are identified in U.S.Pat. Nos. 4,663,220 and 5,304,599, hereby incorporated by reference.

[0029] It is an important feature of the elastomeric material that thereis substantially no diblock polymer present. The presence of anyappreciable amount of diblock may adversely affect the elasticity of thecomposite and web formed therefrom.

[0030] The elastomeric polymer is formed into a nonwoven web accordingto any of several procedures known to those skilled in the art, such as,but not limited to, continuous filament or strand extrusion, and thelike.

[0031] The first and second layers are composed of nonelastic nonwovenpolymer fibers. The fibers are preferably spunbond, but can be producedby other processes known to those skilled in the art.

[0032] The intermediate elastic nonwoven web comprises a layer ofamorphous polymer fibers. The polymer composition desirably comprises anelastomer and may further include a tackifier or other bonding aid toimprove adhesion between the intermediate nonwoven web and the opposedfilm and outer nonwoven layer(s). Examples of suitable polymers include,but are not limited to, elastomeric polyolefins, ethylene-vinyl acetate(EVA), EPDM rubbers, ethylene-ethyl acrylate (EEA), ethylene acrylicacid (EAA), ethylene methyl acrylate (EMA), polyurethane (PU), polyamidepolyether block copolymers, block copolymers having the general formulaA-B-A′ or A-B like copoly(styrene/ethylene-butylene),polystyrene-poly(ethylene-propylene)-polystyrene,polystyrene-poly(ethylene-butylene)-polystyrene, and the like.

[0033] In a preferred embodiment, the amorphous polymer comprises one ormore elastic polyolefins such as a low density polyethylene elastomer,elastic polypropylene, flexible polyolefins, and tackified polymers suchas styrenic block copolymers, polyurethanes or block polyamidepolyethers. In one aspect of the present invention the intermediateelastic nonwoven web comprises, at least in part, a low densityelastomeric polyolefin polymer component such as, for example, a lowdensity ethylene elastomer component having a density less than 0.89g/cm³. Desirably the ethylene elastomer comprises a substantially linearethylene which has a density less than 0.89 g/cm³, desirably from about0.86 g/cm³ to about 0.88 g/cm³ and even more desirably about 0.87 g/cm³.The ethylene elastomer preferably comprises at least about 50% by weightof the polymeric portion of the bonding layer, and more desirable fromabout 70% to about 100% by weight. Preferably the ethylene elastomercomprises a polymer wherein the ethylene monomers are polymerized withan alpha-olefin such that the resulting polymer composition has a narrowmolecular weight distribution ({overscore (M)}_(w)/{overscore (M)}_(n))of about 2, homogeneous branching and controlled long chain branching.Suitable alpha-olefins include, but are not limited to, 1-octene,1-butene, 1-hexene and 4-methyl-pentene. Exemplary polymers includethose which are known in the art as “metallocene,” “constrainedgeometry” or “single-site” catalyzed polymers such as those described inU.S. Pat. No. 5,472,775 to Obijeski et al.; Us. Pat. No. 5,451,450 toErderly et al.; U.S. Pat. No. 5,539,124 to Etherton et al.; and U.S.Pat. No. 5,554,775 to Krishnamurti et al.; the entire contents of whichare incorporated herein by reference.

[0034] The metallocene process generally uses a metallocene catalystwhich is activated, i.e., ionized, by a co-catalyst. Examples ofmetallocene catalysts include bis(n-butylcyclopentadienyl)titaniumdichloride, bis(n-butylcyclopentadienyl)zirconium dichloride,bis(cyclopentadienyl)scandium chloride, bis(indenyl)zirconiumdichloride, bis(methylcyclopentadienyl)titanium dichloride,bis(methylcyclopentadienyl)zirconium dichloride, cobaltocene,cyclopentadienyltitanium trichloride, ferrocene, hafnocene dichloride,isopropyl(cyclopentadienyl,-1-fluorenyl)zirconium dichloride,molybdocene dichloride, nickelocene, niobocene dichloride, ruthenocene,titanocene dichloride, zirconocene chloride hydride, zirconocenedichloride, among others. A more exhaustive list of such compounds isincluded in U.S. Pat. No. 5,374,696 to Rosen et al. and assigned to theDow Chemical Company. Such compounds are also discussed in U.S. Pat. No.5,064,802 to Stevens et al. and also assigned to Dow. However, numerousother metallocene catalysts, single site catalysts, constrained geometrycatalysts and/or similar catalyst systems are known in the art; see forexample, The Encyclopedia of Chemical Technology, Kirk-Othemer, FourthEdition, vol. 17, Olefinic Polymers, pp. 765-767 (John Wiley & Sons1996); the contents of which are incorporated herein by reference.

[0035] Regarding elastomeric polymers, U.S. Pat. No. 5,204,429 toKaminsky et al. describes a process which may produce elastic copolymersfrom cycloolefins and linear olefins using a catalyst which is astereorigid chiral metallocene transition metal compound and analuminoxane. U.S. Pat. Nos. 5,278,272 and 5,272,236, both to Lai et al.,assigned to Dow Chemical and entitled “Elastic Substantially LinearOlefin Polymers” describe polymers having particular elastic properties,the entire contents of which are incorporated herein by reference.Suitable low density ethylene elastomers are commercially available fromDow Chemical Company of Midland, Michigan under the trade nameAFFINITY™, including AFFINITY™ EG8200 (5 MI), XU 58200.02 (30 MI), XU58300.00 (10 MI) and from Exxon Chemical Co. of Houston, Tex. under thetrade name EXAC™ 4049 (4.5 MI, 0.873 g/cm³); 4011 (2.2 MI, 0.888 g/cm³);4041 (3 MI, 0.878 g/cm³); 4006 (10 MI, 0.88 g/cm³).

[0036] In addition, it is believed that the intermediate elastomericfibrous layer may comprise a polymer blend of the amorphous polymer withone or more other polymers which comprise up to about 75% by weight ofthe fiber and more desirably up to about 50% of the fiber. It isbelieved that the fibers may comprise a low density polyethyleneelastomer and additional thermoplastic polymers, desirably higherdensity and/or more crystalline polyolefins. Polyolefins that may besuitable for use with the present invention include, but are not limitedto, LLDPE (density between about 0.90 g/cm³-0.92 g/cm³), LDPE(0.915-0.925 g/cm³, ethylene-propylene copolymers, ethylene vinylacetate, ethylene ethyl acrylate, ethylene acrylic acid, ethylene methylacrylate and the like.

[0037] Examples of additional commercially available elastic polymersinclude, but are not limited to, Himont CATALLOY KS350, KS357 and KS359.Himont Catalloy polymer is an olefinic multistep reactor product whereinan amorphous ethylene propylene random copolymer is molecularlydispersed in a predominantly semicrystalline high propylene monomer/lowethylene monomer continuous matrix, such as described in U.S. Pat. No.5,300,365 to Ogale. In addition, useful elastomeric resins include blockcopolymers having the general formula A-B-A′ or A-B, where A and A′ areeach a thermoplastic polymer endblock which contains a styrenic moietysuch as a poly (vinyl arene) and where B is an elastomeric polymermidblock such as a conjugated diene or a lower alkene polymer. Blockcopolymers of the A-B-A′ type can have different or the samethermoplastic block polymers for the A and A′ blocks, and the presentblock copolymers are intended to embrace linear, branched and radialblock copolymers. In this regard, the radial block copolymers may bedesignated (A-B)_(m)—X, wherein X is a polyfunctional atom or moleculeand in which each (A-B)_(m)—radiates from X in a way that A is anendblock or A_(m)-B_(n), where m may or may not equal n. In the radialblock copolymer, X may be an organic or inorganic polyfunctional atom ormolecule and m is an integer having the same value as the functionalgroup originally present in X. It is usually at least 3, and isfrequently 4 or 5, but not limited thereto. Thus, in the presentinvention, the expression “block copolymer,” and particularly “A-B-A′”and “A-B” block copolymer, is intended to embrace all block copolymershaving such rubbery blocks and thermoplastic blocks as discussed above,which can be extruded (e.g., by meltblowing), and without limitation asto the number of blocks. The elastomeric nonwoven web may be formedfrom, for example, elastomeric(polystyrene/poly(ethylene-butylene)/polystyrene) block copolymers.Commercial examples of such elastomeric copolymers are, for example,those known as KRATON™ materials which are available from Shell ChemicalCompany of Houston, Tex. KRATON™ block copolymers are available inseveral different formulations, a number of which are identified in U.S.Pat. Nos. 4,663,220 and 5,304,599, the entire contents of which arehereby incorporated by reference.

[0038] Polymers composed of an elastomeric A-B-A-B tetrablock copolymermay also be used in the practice of this invention. Such polymers arediscussed in U.S. Pat. No. 5,332,613 to Taylor et al. In such polymers,A is a thermoplastic polymer block and B is an isoprene monomer unithydrogenated to substantially a poly(ethylene-propylene) monomer unit.An example of such a tetrablock copolymer is apolystyrene-poly(ethylene-propylene)-polystyrene-poly(ethylene-propylene)or SEPSEP elastomeric block copolymer available from the Shell ChemicalCompany of Houston, Tex. under the trade designation KRATON™.

[0039] Other exemplary elastomeric materials which are believed suitablefor use with the present invention include polyurethane elastomericmaterials such as, for example, those available under the trademarkESTANE™ from B. F. Goodrich & Co. or MORTHANE™ from Morton ThiokolCorp., polyester elastomeric materials such as, for example, thoseavailable under the trade designation HYTREL™ from E. I. DuPont DeNemours & Company, and those known as ARNITEL™ formerly available fromAkzo Plastics of Arnhem, Holland and now available from DSM of Sittard,Holland.

[0040] In order to improve the thermal compatibility of the intermediatenonwoven web with those of the adjoining layers, it may be desirable toadd a tackifier or bonding aid to the elastic polymer composition.Examples of suitable tackifiers include, but are not limited to thosedescribed in U.S. Pat. No. 4,789,699 to Kieffer et al. Examples ofcommercially available tackifiers are REGALREZ™ 1126 available fromHercules Inc. of Wilmington, DE; ESCOREZ™ 5300 from Exxon Chemical Co.and WINGTACK™ 95 from Goodyear Chemical Co. of Akron, Ohio. The amountof tackifier added will vary with respect to the particular elasticpolymer employed in the intermediate elastic fiber layer and thosepolymers comprising adjoining layers. Although the amount of tackifieradded to the elastic intermediate layer will vary, often addition ofabout 5 to about 20% by weight of the polymer composition is desirable.

[0041] In a preferred embodiment, the intermediate elastic nonwoven webcomprises a matrix of fibers, such as a web of meltblown fibers. In afurther aspect the fibrous elastic layer may comprise a layer ofspunbond fibers and/or staple length fibers of similar basis weight,desirably the nonwoven web has a basis weight of between about 10 g/m²and about 100 g/m², and more desirably a basis weight between about 25g/m² and about 60 g/m². The selection of the basis weight will vary withrespect to the basis weight of the overall laminate as well as therecovery properties of the film and/or outer nonwoven layer. Where boththe outer nonwoven layer and film are extensible but inelasticmaterials, a higher basis weight intermediate/medial elastic fiber layerwill often be required to provide an overall laminate with elasticproperties. However, where the film and/or outer nonwoven layer is alsoelastic, the intermediate elastic web can comprise less of the overalllaminate basis weight.

[0042] Useful elastomeric resins include, but are not limited to, blockcopolymers having the general formula A-B-A′ or A-B, where A and A′ areeach a thermoplastic polymer endblock which contains a styrenic moietysuch as a poly(vinyl arene) and where B is an elastomeric polymermidblock such as a conjugated diene or a lower alkene polymer. Blockcopolymers of the A-B-A′ type can have different or the samethermoplastic block polymers for the A and A′ blocks, and the presentblock copolymers are intended to embrace linear, branched and radialblock copolymers. In this regard, the radial block copolymers may bedesignated (A-B)_(m)-X, wherein X is a polyfunctional atom or moleculeand in which each (A-B)_(m)- radiates from X in a way that A is anendblock. In the radial block copolymer, X may be an organic orinorganic polyfunctional atom or molecule and m is an integer having thesame value as the functional group originally present in X. It isusually at least 3, and is frequently 4 or 5, but not limited thereto.Thus, in the present invention, the expression “block copolymer,” andparticularly A-B-A′ and A-B block copolymer, is intended to embrace allblock copolymers having such rubbery blocks and thermoplastic blocks asdiscussed above, which can be extruded (e.g., by meltblowing and sheetforming), and without limitation as to the number of blocks. Theelastomeric nonwoven web may be formed from, for example, elastomeric(polystyrene/poly(ethylene-butylene)/polystyrene) block copolymers.Commercial examples of such elastomeric copolymers are, for example,those known as KRATON® materials which are available from Shell ChemicalCompany of Houston, Tex. KRATON® block copolymers are available inseveral different formulations, a number of which are identified in U.S.Pat. Nos. 4,663,220 and 5,304,599, hereby incorporated by reference.

[0043] Polymers composed of an elastomeric A-B-A-B tetrablock copolymermay also be used in the practice of this invention as the elastic layer.Such polymers are discussed in U.S. Pat. No. 5,332,613 to Taylor et al.In such polymers, A is a thermoplastic polymer block and B is anisoprene monomer unit hydrogenated to a substantially apoly(ethylene-propylene) monomer unit. An example of such a tetrablockcopolymer is apolystyrene-poly(ethylene-propylene)-polystyrene-poly(ethylene-propylene)or SEPSEP elastomeric block copolymer available from the Shell ChemicalCompany of Houston, Tex. under the trademark KRATON®.

[0044] Other exemplary elastomeric materials which may be used includepolyurethane elastomeric materials such as, for example, those availableunder the trademark ESTANE® from B. F. Goodrich & Co. or MORTHANE® fromMorton Thiokol Corp., polyester elastomeric materials such as, forexample, those available under the trade designation HYTREL® from E. I.DuPont De Nemours & Company, and those known as ARNITEL®, formerlyavailable from Akzo Plastics of Arnhem, Holland and now available fromDSM of Sittard, Holland.

[0045] Another suitable material is a polyester block amide copolymerhaving the formula:

[0046] where n is a positive integer, PA represents a polyamide polymersegment and PE represents a polyether polymer segment. In particular,the polyether block amide copolymer has a melting point of from about150° C. to about 170° C., as measured in accordance with ASTM D-789; amelt index of from about 6 grams per 10 minutes to about 25 grams per 10minutes, as measured in accordance with ASTM D-1238, condition Q (235C/1 Kg load); a modulus of elasticity in flexure of from about 20 MPa toabout 200 MPa, as measured in accordance with ASTM D-790; a tensilestrength at break of from about 29 MPa to about 33 MPa as measured inaccordance with ASTM D-638 and an ultimate elongation at break of fromabout 500 percent to about 700 percent as measured by ASTM D-638. Aparticular embodiment of the polyether block amide copolymer has amelting point of about 152° C. as measured in accordance with ASTMD-789; a melt index of about 7 grams per 10 minutes, as measured inaccordance with ASTM D-1238, condition Q (235 C/1 Kg load); a modulus ofelasticity in flexure of about 29.50 MPa, as measured in accordance withASTM D-790; a tensile strength at break of about 29 MPa, a measured inaccordance with ASTM D-639; and an elongation at break of about 650percent as measured in accordance with ASTM D-638. Such materials areavailable in various grades under the trade designation PEBAX® from ELFAtochem Inc., Philadelphia, Pa. Examples of the use of such polymers maybe found in U.S. Pat. No. 4,724,184, 4,820,572 and 4,923,742 herebyincorporated by reference, to Killian et al. and assigned to the sameassignee as this invention. Elastomeric polymers also include copolymersof ethylene and at least one vinyl monomer such as, for example, vinylacetates, unsaturated aliphatic monocarboxylic acids, and esters of suchmonocarboxylic acids. The elastomeric copolymers and formation ofelastomeric nonwoven webs from those elastomeric copolymers aredisclosed in, for example, U.S. Pat. No. 4,803,117.

[0047] The thermoplastic copolyester elastomers includecopolyetheresters having the general formula:

[0048] where “G” is selected from the group consisting ofpoly(oxyethylene)-alpha,omega-diol, poly(oxypropylene)-alpha,omega-diol,poly(oxytetramethylene)-alpha,omega-diol and “a” and “b” are positiveintegers including 2, 4 and 6, ” m” and “n” are positive integersincluding 1-20. Such materials generally have an elongation at break offrom about 600 percent to 750 percent when measured in accordance withASTM D-638 and a melt point of from about 350° F. to about 400° F. (176to 205° C.) when measured in accordance with ASTM D-2117.

[0049] Commercial examples of such copolyester materials are, forexample, those known as ARNITEL®, formerly available from Akzo Plasticsof Arnhem, Holland and now available from DSM of Sittard, Holland, orthose known as HYTREL(which are available from E.I. duPont de Nemours ofWilmington, Del. Formation of an elastomeric nonwoven web from polyesterelastomeric materials is disclosed in, for example, U.S. Pat. No.4,741,949 to Morman et al. and U.S. Pat. No. 4,707,398 to Boggs.

[0050] In a preferred embodiment, the laminate of the present inventionis formed by sandwiching an elastic layer between two layers ofnonelastic webs. FIG. 1 shows an apparatus for forming the laminate ofthe present invention in which, in general a continuous filament stretchbonded laminate is formed. An example of this process is described inU.S. Pat. No. 5,385,775, issued to Wright et al., the disclosure ofwhich is incorporated by reference herein. The process is generallyrepresented by reference numeral 100. In forming the fibers and thefilaments which are used in the elastic fibrous web, pellets or chips,etc. (not shown) of an extrudable elastomeric polymer are introducedinto a pellet hoppers 102 and 104 of extruders 106 and 108.

[0051] Each extruder has an extrusion screw (not shown) which is drivenby a conventional drive motor (not shown). As the polymer advancesthrough the extruder, due to rotation of the extrusion screw by thedrive motor, it is progressively heated to a molten state. Heating thepolymer to the molten state may be accomplished in a plurality ofdiscrete steps with its temperature being gradually elevated as itadvances through discrete heating zones of the extruder 106 toward ameltblowing die 110 and extruder 108 toward a continuous filamentforming means 112. The meltblowing die 110 and the continuous filamentforming means 112 may be yet another heating zone where the temperatureof the thermoplastic resin is maintained at an elevated level forextrusion. Heating of the various zones of the extruders 106 and 108 andthe meltblowing die 110 and the continuous filament forming means 112may be achieved by any of a variety of conventional heating arrangements(not shown).

[0052] The elastomeric filament component of the anisotropic elasticfibrous web may be formed utilizing a variety of extrusion techniques.For example, the elastic filaments may be formed utilizing one or moreconventional meltblowing die arrangements which have been modified toremove the heated gas stream (i.e., the primary air stream) which flowsgenerally in the same direction as that of the extruded threads toattenuate the extruded threads. This modified meltblowing diearrangement 112 usually extends across a foraminous collecting surface114 in a direction which is substantially transverse to the direction ofmovement of the collecting surface 114. The modified die arrangement 112includes a linear array 116 of small diameter capillaries aligned alongthe transverse extent of the die 112 with the transverse extent of thedie being approximately as long as the desired width of the parallelrows of elastomeric filaments which is to be produced. That is, thetransverse dimension of the die is the dimension which is defined by thelinear array of die capillaries. Typically, the diameter of thecapillaries will be on the order of from about 0.01 inches to about 0.02inches, for example, from about 0.0145 to about 0.018 inches. From about5 to about 50 such capillaries will be provided per linear inch of dieface. Typically, the length of the capillaries will be from about 0.05inches to about 0.20 inches, for example, about 0.113 inches to about0.14 inches long. A meltblowing die can extend from about 20 inches toabout 60 or more inches in length in the transverse direction.

[0053] Since the heated gas stream (i.e., the primary air stream) whichflows past the die tip is greatly reduced or absent, it is desirable toinsulate the die tip or provide heating elements to ensure that theextruded polymer remains molten and flowable while in the die tip.Polymer is extruded from the array 116 of capillaries in the modifieddie 112 to create extruded elastomeric filaments 118.

[0054] The extruded elastomeric filaments 118 have an initial velocityas they leave the array 116 of capillaries in the modified die 112.These filaments 118 are deposited upon a foraminous surface 114 whichshould be moving at least at the same velocity as the initial velocityof the elastic filaments 118. This foraminous surface 114 is an endlessbelt conventionally driven by rollers 120. The filaments 118 aredeposited in substantially parallel alignment on the surface of theendless belt 114 which is rotating as indicated by the arrow 122. Vacuumboxes (not shown) may be used to assist in retention of the matrix onthe surface of the belt 114. The tip of the die 112 is should be asclose as practical to the surface of the foraminous belt 114 upon whichthe continuous elastic filaments 118 are collected. For example, thisforming distance may be from about 2 inches to about 8 inches.Desirably, this distance is from about 2 inches to about 8 inches.

[0055] It may be desirable to have the foraminous surface 114 moving ata speed that is much greater than the initial velocity of the elasticfilaments 118 in order to enhance the alignment of the filaments 118into substantially parallel rows and/or elongate the filaments 118 sothey achieve a desired diameter. For example, alignment of theelastomeric filaments 118 may be enhanced by having the foraminoussurface 114 move at a velocity from about 2 to about 10 times greaterthan the initial velocity of the elastomeric filaments 118. Even greaterspeed differentials may be used if desired. While different factors willaffect the particular choice of velocity for the foraminous surface 114,it will typically be from about four to about eight times faster thanthe initial velocity of the elastomeric filaments 118.

[0056] Desirably, the continuous elastomeric filaments are formed at adensity per inch of width of material which corresponds generally to thedensity of capillaries on the die face. For example, the filamentdensity per inch of width of material may range from about 10 to about120 such filaments per inch width of material. Typically, lowerdensities of filaments (e.g., 10-35 filaments per inch of width) may beachieved with only one filament forming die. Higher densities (e.g.,3-120 filaments per inch of width) may be achieved with multiple banksof filament forming equipment.

[0057] The meltblowing fiber component of the anisotropic elasticfibrous web is formed utilizing a conventional meltblowing processrepresented by reference numeral 124. Meltblowing processes generallyinvolve extruding a thermoplastic polymer resin through a plurality ofsmall diameter capillaries of a meltblowing die as molten threads into aheated gas stream (the primary air stream) which is flowing generally inthe same direction as that of the extruded threads so that the extrudedthreads are attenuated, i.e., drawn or extended, to reduce theirdiameter. Such meltblowing techniques, and apparatus therefor, arediscussed fully in U.S. Pat. No. 4,663,220, the contents of which areincorporated herein by reference.

[0058] In the meltblowing die arrangement 110, the position of airplates which, in conjunction with a die portion define chambers andgaps, may be adjusted relative to the die portion to increase ordecrease the width of the attenuating gas passageways so that the volumeof attenuating gas passing through the air passageways during a giventime period can be varied without varying the velocity of theattenuating gas. Generally speaking, lower attenuating gas velocitiesand wider air passageway gaps are generally preferred if substantiallycontinuous meltblowing fibers or microfibers are to be produced.

[0059] The two streams of attenuating gas converge to form a stream ofgas which entrains and attenuates the molten threads as they exit theorifices, into fibers depending upon the degree of attenuation,microfibers, of a small diameter which is usually less than the diameterof the orifices. The gas-borne fibers or microfibers 126 are blown, bythe action of the attenuating gas, onto a collecting arrangement which,in the embodiment illustrated in FIG. 1, is the foraminous endless belt114 which carries the elastomeric filament in substantially parallelalignment. The fibers or microfibers 126 are collected as a coherentmatrix of fibers on the surface of the elastomeric filaments 118 andforaminous endless belt 114 which is rotating as indicated by the arrow122. If desired, the meltblowing fibers or microfibers 126 may becollected on the foraminous endless belt 114 at numerous impingementangles. Vacuum boxes (not shown) may be used to assist in retention ofthe matrix on the surface of the belt 114. Typically the tip 128 of thedie 110 is from about 6 inches to about 14 inches from the surface ofthe foraminous belt 116 upon which the fibers are collected. Theentangled fibers or microfibers 124 autogenously bond to at least aportion of the elastic continuous filaments 118 because the fibers ormicrofibers 124 are still somewhat tacky or molten while they aredeposited on the elastic continuous filaments 118, thereby forming theanisotropic elastic fibrous web 130.

[0060] At this point, it may be desirable to lightly calendar theelastic fibrous web of meltblowing fibers and filaments in order toenhance the autogenous bonding. This calendering may be accomplishedwith a pair of nip rolls 132 and 134 under sufficient pressure (andtemperature, if desired) to cause permanent autogenous bonding betweenthe elastomeric filaments and the elastomeric meltblown fibers.

[0061] As discussed above, the elastomeric filaments and elastomericmeltblowing fibers are deposited upon a moving foraminous surface. Inone embodiment of the invention, meltblown fibers are formed directly ontop of the extruded elastomeric filaments. This is achieved by passingthe filaments and the foraminous surface under equipment which producesmeltblown fibers. Alternatively, a layer of elastomeric meltblown fibersmay be deposited on a foraminous surface and substantially parallel rowsof elastomeric filaments may be formed directly upon the elastomericmeltblown fibers. Various combinations of filament forming and fiberforming equipment may be set up to produce different types of elasticfibrous webs. For example, the elastic fibrous web may containalternating layers of elastomeric filaments and elastomeric meltblowingfibers. Several dies for forming meltblown fibers or creatingelastomeric filaments may also be arranged in series to providesuperposed layers of fibers or filaments.

[0062] The elastomeric meltblown fibers and elastomeric filaments may bemade from any material which may be manufactured into such fibers andfilaments. Generally, any suitable elastomeric fiber forming resins orblends containing the same may be utilized for the elastomeric meltblownfibers and any suitable elastomeric filament forming resins or blendscontaining the same may be utilized for the elastomeric filaments. Thefibers and filaments may be formed from the same or differentelastomeric resin. Tackifiers and/or pressure sensitive adhesives may beincorporated into the meltblown polymer.

[0063] A first spunbond layer 136 and a second spunbond layer 138 areunwound from takeup rolls 140 and 142, respectively, and fed through thecalendar rolls 132 and 134 on either side of the web 130. As the threelayers are passed through the calendar rolls 132 and 134 the material islaminated together by adhesive forces and now form the compositematerial 144.

[0064] The web 130 is stretched to add tension as it is removed from theforaminous surface 114, i.e., by having the speed of the calendar rolls132 and 134 being set faster than the linear speed of the foraminoussurface 114, as is known to those skilled in the art. After thecomposite web 144 exits the calendar rolls 132 and 134, it is relaxed bypassing the web 144 through a second set of calendar rolls 144 and 146,which are operating at a speed slower than the calendar rolls 132 and134, thus inducing a relaxing of the fibers. The resulting web isfurther processed or removed onto a takeup roll (not shown). It is to beunderstood by those skilled in the art that additional guide rolls orthe like may be used for more control or convenient processing of thematerial of the present invention.

[0065] The continuous filament process is the preferred process to formfilaments of the elastomeric triblock polymer layer of the presentinvention because of the high molecular weight of the polymer, whichtends to produce poorer quality meltblown filaments. It is possible thatother components can be used to permit quality meltblown filaments to beproduced, or to modify the meltblown die or apparatus to accommodatehigher molecular weight polymers. But, since heretofore such materialsas described in the present disclosure have not been used successfullyin a meltblown process, the continuous filament process was used.Additionally, the composite material of the present invention canincorporate a plurality of layers of each of the individual layers ofmaterial. For example, two layers of meltblown material can sandwich thefilaments. Or, two filament layers can sandwich a single meltblownlayer. Different combinations and sequences of the layers is anticipatedas being possible, depending on the ultimate properties desired.

[0066] The modified material used in the elastic layer of the presentinvention provides improved elastic properties. The increased molecularweight of the midblock portion of the A-B-A′ polymer results inincreased persistence length of the polymer chains. The increase in theoverall molecular weight also increases entanglement density, whichincreases the time for segments uncoil or disentangle. The increase inentanglement also reduces slippage of the midblock domain. Relaxationtime is correspondingly increased. All these factors favor theimprovement of the elastic character of the polymer of the presentinvention. The absence of the diblock polymer also improves thestress-relaxation behavior because the lack of plasticizing affect theircompatibilization of the styrene and rubber block.

[0067] The present invention provides a continuous filament stretchbonded laminate (“CFSBL”) material having lower cost and betterperformance than conventional CFSBL materials based on tetrablock KRATONpolymers, when used at body temperature.

[0068] While the invention has been described in connection with certainpreferred embodiments, it is not intended to limit the scope of theinvention to the particular forms set forth, but, on the contrary, it isintended to cover such alternatives, modifications, and equivalents asmay be included within the spirit and scope of the invention as definedby the appended claims. The invention will be further described inconnection with the following examples, which are set forth for purposesof illustration only. Parts and percentages appearing in such examplesare by weight unless otherwise stipulated.

EXAMPLES

[0069] Test Procedures

[0070] Stress-Elongation

[0071] Samples used for stress-elongation test were in the in the formof a strand or fiber. The strand was clamped in the jaws of a MaterialsTesting System (MTS) Sintech 1/S tensile testing frame. A grip to gripdistance of 3 inches was used in all tests. The samples were displacedat a rate of 2 inches/minute via the cross-head movement.

[0072] From a knowledge of the initial cross-sectional area and theinitial grip-to-grip distance the engineering stress and the percentage(%) elongation were calculated. From the stress-elongation data, theinitial shear modulus was calculated using rubber elasticity theory. Theyield stress, the stress at break and elongation at break were alsoobtained from the normalized data.

[0073] Stress Relaxation

[0074] The stress relaxation test was also carried out on a MTS Sintech1/S tensile test frame. The test specimen was clamped between the jawsat a 3″ grip to grip distance. The sample and the grip fixtures wereenclosed in an environmental chamber. The sample, after clamping, wasequilibrated at 100° F. for 3 minutes. The sample was then elongated toa final constant elongation of 4.5 inches (50% elongation) at across-head displacement speed of 20″/minute. The load required tomaintain the 50% elongation as a function of time was monitored. Thedata was acquired using the MTS Sintech Test Works data acquisitioncapability.

[0075] The data thus obtained was reduced by calculating the engineeringstress (lb/in², psi) from a knowledge of the initial cross-sectionalarea of the sample. Strain (elongation) was calculated from the initialgrip-to-grip distance and the constant elongation. Ratio of the stressand strain gives the stress relaxation modulus (psi). The data wasfitted to the power-law model given below to obtain, a materialcharacteristic, the exponent m.

σ=σ_(t=0.1 min)t^(−m)

[0076] Another parameter that was also obtained from this experiment wasthe percentage loss of load at the end of the experiment. The load losswas obtained from a knowledge of the initial load and final load usingthe following equation:$\frac{\left( {{{INITIAL}\quad {LOAD}} - {{FINAL}\quad {LOAD}}} \right)}{{INITIAL}\quad {LOAD}} \times 100$

[0077] Equilibrium Hysteresis

[0078] The equilibrium hysteresis was obtained by cycling the samplesbetween zero and 100% elongation. The MTS Sintech 1/S screw driven framewas used for the acquisition of the hysteresis data. The cross-head wasdisplaced at a rate of 20 in./min. The samples were cycled 10 times. Thedata acquired was at a rate of 100 data points per cycle. The loadingand unloading energy were calculated by integrating the area under therespective. Percentage hysteresis was then calculated according to thefollowing equation.${\% \quad {HYSTERESIS}} = {\frac{\left( {{{LOADING}\quad {ENERGY}} - {{UNLOADING}\quad {ENERGY}}} \right)}{{LOADING}{\quad \quad}{ENERGY}} \times 100}$

[0079] Tension Set

[0080] In this intermittent stress-elongation experiment, a sample isstretched to a predetermined elongation, released and then stretched tothe next greater degree of elongation and so on. The remaining strain ata given time after the removal of the applied stress is then measured.The tension set gives a measure of the irreversibility of thedeformation.

[0081] Dynamic Mechanical Thermal Analysis (“DMTA”)

[0082] DMTA is an analytical tool known to those skilled in the art foranalyzing the storage modulus of a fabric and a detailed review of thetechnique is not needed. Briefly however, storage modulus is plottedagainst temperature and the tangent delta (“tan δ”). In a given plot ofa material there is an area known as the “rubbery plateau,” a flattenedarea of the curve, which related to the dimensional stability of thepolymer. A longer rubbery plateau is indicative of a more stablepolymer. The rubbery plateau of a given material is lower for a lowermolecular weight and higher for a higher molecular weight.

[0083] As the molecular weight of the triblock copolymer midblockincreases, the softness of the polymer increases, as indicated by adecreased modulus.

[0084] The tan δ is a ratio of the loss modulus to the storage modulus.The higher molecular weight material will have a higher and sharper peaktan δ, which is more desirable. A sharp transition indicates that thehard styrene domain is well phase segregated, which is desirable.

Example 1

[0085] Sample 1 was a CFSBL fabric, wherein the continuous filamentswere produced from KRATON RP6608, a SEPS triblock polymer having anumber average molecular weight of about 81,000 g/mol, containing atackifier and polyethylene wax. Sample 2 was a control, a CFSBL fabric,wherein the continuous filaments were produced from KRATON RP 6588SEPSEP tetrablock polymer, containing a tackifier and polyethylene wax.Sample 3 was a CFSBL fabric, wherein the continuous filaments wereproduced from a KRATON SEPS triblock polymer having a number averagemolecular weight of about 61,000 g/mol, containing a tackifier andpolyethylene wax. The sample fabrics were produced according to theprocess described above, where the process parameters are set forth inFIG. 2. FIGS. 3-5 show various process parameters for different materialruns. TABLE 1 STRESS-ELONGATION BEHAVIOR AT BODY TEMPERATURE SAMPLE IDMODULUS (psi) σ_(y) (%) λ_(y) (%) STS (%) Sample 1 92 25 18 227 Sample 291 18 14 174

[0086] σ_(y) is stress at yield; γ_(y) is elongation at yield; STS is“stretch to stop,” i.e., the elastic limit before the spunbond layertakes over the stress-elongation behavior. The test results indicatedthat the stress at yield was about 39% better for the triblock comparedto the tetrablock polymer. The elongation at yield was about 28% betterfor the triblock. The stretch to stop data was about 30% improved forthe triblock. TABLE 2 HYSTERESIS BEHAVIOR AT BODY TEMPERATURE SAMPLE IDH₁(%) H₃(%) H₇(%) H₁₀(%) Sample 1 16 10 10 9 Sample 2 24 17 16 16

[0087] TABLE 3 HYSTERESIS BEHAVIOR AT ROOM TEMPERATURE SAMPLE ID H₁(%)H₃(%) H₇(%) H₁₀(%) Sample 1 20 12 11 11 Sample 2 29 19 19 18

[0088] H_(I) is the hysteresis of the I^(th) cycle. i=1,3,7,10. Lowerhysteresis numbers indicate better elasticity properties of the fabric.The control Sample 2 had higher hysteresis and resulting poorerelasticity than Sample 1. TABLE 4 TENSION SET BEHAVIOR AT BODYTEMPERATURE SAMPLE ID S(25%) S(50%) S(100%) S(200%) S(300%) Sample 1 1 23 8 8 Sample 2 1 2 4 26 24

[0089] TABLE 5 TENSION SET BEHAVIOR AT ROOM TEMPERATURE SAMPLE ID S(25%)S(50%) S(100%) S(200%) S(300%) Sample 1 1 2 4 7 11 Sample 2 1 2 6 21 39

[0090] S is the tension set. Higher tension set indicates poorer elasticproperties. Beyond 100% the control Sample 2 numbers are significantlypoorer than Sample 1. Over a longer period of time at body temperatureSample 1 will have better elastic behavior than control Sample 2. TABLE6 12 HRS. STRESS RELAXATION BEHAVIOR AT BODY TEMPERATURE SAMPLE ID LOADDECAY SLOPE LOAD LOSS (%) Sample 1 −0.08 40 Sample 2 −0.10 52 Sample 3−0.10 52

[0091] Lower numbers indicate better elastic behavior. The differencebetween the samples is significant. The difference of 0.02 in slopebetween Sample 1 and Samples 2 and 3 is remarkable because therelationship in slope is an exponential one.

[0092]FIG. 3 is a graph of the storage modulus, E′, measured in dyn/cm²,plotted against temperature (in ° C.), and tan δ. The lower molecularweight Sample 3 is shown in solid circles and the higher molecularweight Sample 1 is shown in open circles. The sigmoidal curves are themodulus results. The curve peaking at about −50° C. is the tan δ. Thegraph shows a longer and lower modulus of the high molecular weightmaterial is more elastic and has superior properties over the shorterand higher modulus curve of the lower molecular weight material. Thehigher sharp tan δ peak of the higher molecular weight material isindicative of better phase segregation of the styrene domain than in thelower molecular weight material.

[0093] Although only a few exemplary embodiments of this invention havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe following claims. In the claims, means plus function claims areintended to cover the structures described herein as performing therecited function and not only structural equivalents but also equivalentstructures. Thus although a nail and a screw may not be structuralequivalents in that a nail employs a cylindrical surface to securewooden parts together, whereas a screw employs a helical surface, in theenvironment of fastening wooden parts, a nail and a screw may beequivalent structures.

[0094] It should further be noted that any patents, applications orpublications referred to herein are incorporated by reference in theirentirety

What is claimed is:
 1. A composite elastic material having improvedelastic properties at body temperature, comprising: A) a first layer ofsubstantially parallel filaments formed of an elastomeric polymer, saidpolymer having a number average molecular weight of from about 65,000g/mol to about 100,000 g/mol; B) a second layer of elastomeric meltblownfibers, said meltblown fibers bonded to at least a portion of the firstlayer filaments; C) a third layer of spunbond fibers; and, a fourthlayer of spunbond fibers; wherein said first and second layers aredisposed between said third and fourth layers.
 2. The composite elasticmaterial of claim 1, wherein said elastomeric polymer of said firstlayer comprises an A-B-A′ triblock copolymer wherein A and A′ are thesame or different thermoplastic polymer, and wherein B is an elastomericpolymer block.
 3. The composite elastic material of claim 2, wherein Ais a styrene-based polymer.
 4. The composite elastic material of claim2, wherein B is selected from the group consisting of ethylene/propyleneand ethylene/butylene.
 5. The composite elastic material of claim 4,wherein said ethylene/propylene and ethylene/butylene are saturated. 6.The composite elastic material of claim 4, wherein saidethylene/propylene and ethylene/butylene are unsaturated.
 7. Thecomposite elastic material of claim 2, wherein said elastomeric materialcomprises about 18% styrene-based material and about 82% midblockmaterial.
 8. The composite elastic material of claim 1, wherein saidelastomeric polymer of said first layer is substantially free of diblockpolymer.
 9. The composite elastic material of claim 1, wherein saidmaterial has a percent load loss at body temperature over a twelve hourperiod of less than about 40%.
 10. The composite elastic material ofclaim 1, wherein said material has a percent load loss at bodytemperature over a twelve hour period of less than about 50%.
 11. Thecomposite elastic material of claim 1, wherein said material has a loaddecay slope at body temperature over a twelve hour period of about−0.08.
 12. The composite elastic material of claim 1, wherein saidmaterial has a load decay slope at body temperature over a twelve hourperiod of about −0.10.
 13. The composite elastic material of claim 1,wherein said polymer has a number average molecular weight of from about65,000 g/mol to about 100,000 g/mol.
 14. The composite elastic materialof claim 1, wherein said polymer has a number average molecular weightof from about 75,000 g/mol to about 90,000 g/mol.
 15. The compositeelastic material of claim 1, wherein said material has a number averagemolecular weight of about 81,000 g/mol.
 16. The composite elasticmaterial of claim 1, wherein said meltblown fibers comprise anelastomeric polymer selected from the group consisting of elasticpolyesters, elastic polyurethanes, elastic polyamides, elasticcopolymers of ethylene and at least one vinyl monomer, and elasticA-B-A′ block copolymers wherein A and A′ are the same or differentthermoplastic polymers, and wherein B is an elastomeric polymer block.17. The composite elastic material of claim 16, wherein said elastomericpolymer is blended with a processing aid.
 18. The composite elasticmaterial of claim 16, wherein said elastomeric polymer is blended with atackifying resin.
 19. The composite elastic material of claim 1, furthercomprising a fifth layer of meltblown material.
 20. The compositeelastic material of claim 12, wherein said second and said fifth layersof meltblown material are bonded to both sides of said first layer. 21.A process for forming a composite elastic material having improvedelastic properties at body temperature, comprising: A) providing a firstlayer of substantially parallel filaments formed of an elastomericpolymer, said polymer having a number average molecular weight of fromabout 65,000 g/mol to about 100,000 g/mol; B) a second layer ofelastomeric meltblown fibers, said meltblown fibers bonded to at least aportion of the first layer filaments so that the elastic fibrous web isanisotropic; C) adhering said first and said second layers together toform a first web; D) stretching said first web in the machine direction;E) providing a third layer of spunbond fibers; F) providing a fourthlayer of spunbond fibers; and, G) adhering said third and fourth layersto both sides of said first web to form a second web.
 22. The process ofclaim 21, further comprising passing said second web through at leastone pair of calendar rolls.
 23. The process of claim 22, furthercomprising relaxing said second web.
 24. The composite elastic materialof claim 21, wherein said elastomeric polymer of said first layercomprises an A-B-A′ triblock copolymer wherein A and A′ are the same ordifferent thermoplastic polymer, and wherein B is an elastomeric polymerblock.
 25. The composite elastic material of claim 24, wherein A is astyrene-based polymer.
 26. The composite elastic material of claim 24,wherein B is selected from the group consisting of ethylene/propyleneand ethylene/butylene.
 27. The composite elastic material of claim 24,wherein elastomeric material comprises about 18% styrene-based materialand about 82% midblock material.
 28. The composite elastic material ofclaim 21, wherein said elastomeric polymer of said first layer issubstantially free of diblock polymer.
 29. The composite elasticmaterial of claim 21, wherein said material has a percent load loss atbody temperature over a twelve hour period of about 40%.
 30. Thecomposite elastic material of claim 21, wherein said material has a loaddecay slope at body temperature over a twelve hour period of about−0.08.
 31. The composite elastic material of claim 21, wherein saidmeltblown fibers comprise an elastomeric polymer selected from the groupconsisting of elastic polyesters, elastic polyurethanes, elasticpolyamides, elastic copolymers of ethylene and at least one vinylmonomer, and elastic A-B-A′ block copolymers wherein A and A′ are thesame or different thermoplastic polymers, and wherein B is anelastomeric polymer block.
 32. The composite elastic material of claim21, wherein said elastomeric polymer is blended with a processing aid.33. The composite elastic material of claim 21, wherein said elastomericpolymer is blended with a tackifying resin.
 34. The composite elasticmaterial of claim 21, further comprising a fifth layer of meltblownmaterial.
 35. The composite elastic material of claim 34, wherein saidsecond and said fifth layers of meltblown material are bonded to bothsides of said first layer.
 36. An article of manufacture incorporating acomposite elastic material made according to the process of claim 21.37. The article of manufacture of claim 36, wherein said article isselected from the group consisting of, pads, diapers, incontinenceundergarments and personal care products.
 38. A training pants articlehaving side panels incorporating a composite elastic material, saidelastic material comprising: A) a first layer of substantially parallelfilaments formed of an elastomeric polymer, said polymer having a numberaverage molecular weight of from about 65,000 g/mol to about 100,000g/mol; B) a second layer of elastomeric meltblown fibers, said meltblownfibers bonded to at least a portion of the first layer filaments so thatthe elastic fibrous web is anisotropic; C) a third layer of spunbondfibers; and, D) a fourth layer of spunbond fibers; wherein said firstand second layers are disposed between said third and fourth layers. 39.A polymer suitable for use in an elastic material, said polymercomprising an A-B-A′ triblock copolymer wherein A and A′ are the same ordifferent thermoplastic polymer, and wherein B is an elastomeric polymerblock, said polymer having a number average molecular weight of fromabout 65,000 g/mol to about 100,000 g/mol; said A and A′ being astyrene-based polymer and B is selected from the group consisting ofethylene/propylene and ethylene/butylene.
 40. The composite elasticmaterial of claim 39, wherein said elastomeric material comprises about18% A and A′ and about 82% B.